It sounds like the blower motor resistor has gone out but to be sure lets test the system. Here is a blower motor wiring diagram and guide so you can do some testing. 1994 Chevy Lumina Heater Fan Motor. Hi, My Heater Fan Motor Is Going Bad (rumbling).. I am looking for what the wires that plug into the heater/ ac controls do. I have a bad unit and need to bypass the hot cold switch somehow to blow heat.. Since you have already confirmed that the blower switch (on the AC/Heater Control Panel) is sending battery power to the correct connector terminals using a jumper wire to bypass the resistor assembly is a performance check that will check the integrity of the circuits between the blower resistor and blower motor..